1. Field of the Invention
The present invention relates to a multiple-ratio automatic transmission characterized by a swap-shift between at least two transmission ratios.
2. Background Art
Prior art U.S. Pat. Nos. 6,292,731; 5,722,519; 5,553,694; 5,758,302; 6,370,463; and 6,577,939 disclose control systems for the multiple-ratio automatic transmission for an automotive vehicle driveline which establish torque flow paths between the vehicle engine and vehicle traction wheels. The transmission of each of the prior art references uses an overdrive or auxiliary gearset in series relationship with respect to a multiple-ratio geared transmission, sometimes referred to as a main gearset or a Simpson gearset. The transmission is characterized by the so-called swap-shift during upshifts from a second gear ratio to a third gear ratio and from a second gear ratio to a fifth gear ratio as the vehicle is accelerated. Conversely, a swap-shift occurs during downshifts from the third gear ratio to the second gear ratio and from the fifth gear ratio to the second gear ratio.
During a swap-upshift from the second gear ratio to the third gear ratio, the overdrive gearset must be downshifted, while the Simpson gearset is upshifted, the shifts being synchronized or coordinated during shift progression in each gearset. Conversely, a swap-downshift from the third ratio to the second ratio requires a simultaneous upshift of the overdrive gearset and a downshift of the Simpson gearset in a synchronized manner.
Ratio changes in the overdrive gearset are controlled by pressure operated clutches and brakes, as are the ratio changes in the Simpson gearset. In the case of a swap-upshift from the second overall ratio to the third overall ratio, a reaction brake for the overdrive gearset must be released as a reaction brake for the Simpson gearset is applied. Conversely, on a 3-2 swap-downshift, a reaction brake for the Simpson gearset must be released in synchronism with the application of a friction brake for the overdrive gearset.
In the case of a swap-upshift from the second ratio to the fifth ratio, the reaction brake for the overdrive gearset must be released in synchronism with the engagement of a clutch for the Simpson gearset, the latter drivably connecting two gear elements of the Simpson gearset so that the Simpson gearset ratio, following an upshift, is unity.
Transmissions of the kind disclosed in prior art references, under certain operating conditions, cannot achieve precise synchronization of the upshift and the downshift of the two series-related gearsets during a swap-shift. Precise synchronization is required, however, throughout the life of the transmission, notwithstanding vehicle component and environmental variations. Although precise synchronization can initially be achieved by calibration, calibrated synchronism becomes less precise throughout the useful life of the transmission as the transmission ages. This may cause small errors in the upshift and downshift timing of the two gear units. Such errors in synchronism have a significant effect on the overall shift quality. Specifically, gear ratio “flares” and gear ratio “overshoots,” as well as output torque disturbances, can result if synchronization errors develop.